Well, I'm pretty late in and I doubt anyone will read this, but I'll throw in my two cp.
I can't stand Cena, and it all started with his "Thuganomics" and the hip hop crap. Stone Cold for instance, was a redneck in the sense that he always drove a big truck and talked with an accent, but Stone Cold never pushed being a redneck on the fans. By him embracing the hip hop way, he somewhat alienated fans who don't care for that "culture" and annoyed fans like be who have to deal with white guys that think they're the next Eminem on a daily basis.
I currently thnk the belt that was designed for Cena, is a disgrace. Why the hell does a belt have a spinner on it? Its got the bling of a rap video and, well, the spinner. The World Championship/Old WCW belt is what a real championship belt looks like, and I'm honestly suprised the writers haven't cracked on that when they've done championship interactons. Even the ECW belt and the Smoking Skull belt had a more prestigious look to them. In would almost be as if Stone Cold had a belt made with a rebel flag or an old Texas (the country) flag on it.
Moving on to style, his in ring ability is next to none. Even taking a star like Stone Cold, or even Hogan, they at least have "mid-match moves." Stone Cold had the tackle and punch, Hogan has the "Hulk Up," Triple H has the Face Buster, Shawn Michaels has the elbow drop, etc etc. While I know a good chunk of these are used as pre-cursors to the finisher, it's not always the case, especially in PPVs. Cena doesn't have one. Just about every match I've watched, its "Five Knuckle Shuffle" to "STFU." At least he doesn't do that, "You can't see me" crap anymore. The bottom line is, in the ring, he's boring to watch; he's gotten better, but just about every match is the same, and you always know he's going to win. His character hasn't really evolved, and is very similar if not exactly the same to the same character he was when he moved to Raw.
To be honest, I think Cena in a way is more of a marketing project more then anything. They marketed his character in a way that kids and ladies would love him. Guys buy their girlfriends Cena merchandise, girls by their own Cena merchandise, and parents buy it for their kids. Just think about the football Cena Jersey. Everyone loves a football Jersey, and WWE was even personalizing them at shows. This demographic makes up the majority of the merchandise sales, so Cena stays on top while others are only purchased by fans who appreciate someone with skill. Since he is making the most merchanidse sales, WWE thinks everyone loves him, so he stays the champ.
Just my opinion, I could be completely wrong